While the present invention will find application wherever it is desired to adjust the drive ratio between a drive shaft and a driven shaft, it is particularly suited for use in liquid flow metering systems. Such systems commonly employ a positive displacement meter having one or more rotors which rotate through a predetermined angle as a corresponding quantity of liquid flows through the meter. The output shaft of the meter is coupled by a transmission having an adjustable drive ratio to various instruments including a counter which provides a visible indication of the quantity of liquid passed through the meter. In the metering art, such a variable transmission device is commonly referred to as an adjuster. The quantity of liquid actually passed through the meter and the quantity indicated by the counter may differ for many reasons, and the purpose of the adjuster is to make adjustments to compensate for these differences.
An adjuster in the form of an infinitely variable planetary drive mechanism incorporating a plurality of balls which couple an input shaft to an output shaft is disclosed in U.S. Pat. No. 2,868,038. This prior art adjuster has been successfully used in the liquid metering field for many years because of its many desirable features, not the least of which is a linear response curve. However, the required torque capacity of adjusters has increased over the years as the loads on the meter have increased. In addition to the counter, there are now several other devices such as presets, printers and temperature compensators which are commonly stacked on the counter and which must also be driven by the meter. Also, unscrupulous persons have been known to temporarily overload the adjusters so that excessive slippage occurs with consequently false readings appearing on the associated counters and printers. The torque capacity of this prior art adjuster cannot be appreciably increased without greatly increasing its overall size inasmuch as an increase in the internal spring pressure causes the drive balls to jam between the jaws of the outer race. In addition to increasing the torque capacity, it would be desirable to increase the life of the adjuster by reducing wear and tear on the race surfaces.